The present invention relates generally to interface devices for allowing humans to interface with computer systems, and more particularly to low-cost computer interface devices that allow the user to provide input to computer systems and allow computer systems to provide force feedback to the user.
A user can interact with an environment displayed by a computer to perform functions and tasks on the computer, such as playing a game, experiencing a simulation or virtual reality environment, using a computer aided design system, operating a graphical user interface (GUI), navigate web pages, etc. Common human-computer interface devices used for such interaction include a mouse, joystick, trackball, gamepad, steering wheel, stylus, tablet, pressure-sensitive sphere, or the like, that is connected to the computer system controlling the displayed environment. Typically, the computer updates the environment in response to the user's manipulation of a physical manipulandum such as a joystick handle or mouse, and provides visual and audio feedback to the user. The computer senses the user's manipulation of the user object through sensors provided on the interface device that send locative signals to the computer.
In some interface devices, force (kinesthetic) feedback is also provided to the user. These types of interface devices can provide physical sensations which are felt by the user manipulating a user manipulandum of the interface device, such as a joystick handle, mouse, steering wheel, trackball, etc. One or more motors or other actuators are coupled to the manipulandum and are connected to the controlling computer system. The computer system controls forces on the manipulandum in conjunction and coordinated with displayed events and interactions by sending control signals or commands to the actuators. The computer system can thus convey physical force sensations to the user in conjunction with other supplied feedback as the user is grasping or contacting the manipulandum of the interface device.
While kinesthetic force feedback devices offer much to enrich a user's experience, they present many issues as well. One of the difficulties with these types of devices is directly related to how the user manipulates the device. When the user is gripping the manipulandum at full grasping strength, full scale forces can be output to the user with the intended effect. However, if the user is not gripping the manipulandum, the forces will generate undesirable motion on the manipulandum. For example, if the user temporarily rests a hand-held force feedback device on a table and leaves it there, and the manipulandum is still moving from applied forces, the device can bounce around from the motion. For some larger devices, outputting forces and unexpected motion when there is no user contact can also be a safety concern. In other cases, if the user is gripping or contacting the manipulandum very lightly, the forces are of too great a strength and cause too much motion of the manipulandum and/or cause distracting and non-immersive forces on the user. The undesired motion is accentuated if the manipulandum is designed to generate high force output levels for compelling force sensations.
Traditionally, these problems have been partially solved through the use of a “deadman” sensor or switch. The deadman sensor is used to detect when the user is gripping or in contact with the device that is being operated. When the user contact with the manipulandum is detected, the commanded forces are output to the device. However, if the user breaks contact with the manipulandum or device, the force output is stopped until the user makes contact again, at which point the forces resume output if they are still being commanded to play. In some embodiments, as described in U.S. Pat. Nos. 5,691,898 and 5,734,373, incorporated herein by reference, the force feedback device or host computer can slowly ramp up the force magnitudes when the forces resume playing after the user re-contacts the device. This prevents the manipulandum from immediately jerking or moving unpredictably as the user makes contact and allows the user some time to establish a complete, firm grip or contact.
The sensors typically used for deadman operation in a force feedback device are optical sensors. For example, the one type includes a phototransistor detector paired with a light-emitting diode (LED) emitter. In many cases, the LED is pulsed with a known driving signal and the same form (frequency, etc.) of signal must be detected at the detector for a positive detection to have occurred. The pulsing method prevents false triggering levels that may be caused by ambient light in the device's environment. Other optical sensors may include a detector only, which detects skin tone of the user or ambient light. Other types of sensors that can also be used as deadman sensors include capacitive sensors, physical switches or buttons, etc.
The use of this type of deadman sensor is often a good solution for the problem of undesirable motion of a manipulandum that is not being contacted by the user. It works very well to arrest the motion of the manipulandum when the user releases the manipulandum. However, this form of deadman operation has some drawbacks. Since an additional sensor must be added to the device, the overall cost and complexity of the force feedback system is increased. Further, since the sensor will in many cases require support electronics, additional print circuit board space will be required and could possibly increase the size of the force feedback device. Also, the wire routing and assembly for a deadman sensor placed in a moving manipulandum is more complex. For some devices it may be difficult to locate the sensor in a “universal” position on the manipulandum or housing, i.e. a location that will allow the sensor to be activated by the nominal grasping position of all users, especially for smaller devices such as gamepads. Also, there are times where the user may be driven off of the sensor by the motion of the device itself. In these cases, the device may falsely detect deactivations during operation.
In addition, other problems are not at all addressed by existing deadman sensors. The user may be gripping the manipulandum at different strengths during operation of the force feedback device. Forces that feel excellent for a stronger grip may feel far too strong when the player is gripping the manipulandum more lightly, thus causing the user's experience to be downgraded. Existing deadman sensors do not sense the degree of a user's touch, and thus cannot compensate for different degrees of user contact.